Printed electronics keep shirts cool – literally

Cranking up the heat or the air conditioner have been common responses to changes in temperature for decades. But what if the microclimate could be controlled at the individual level? What if clothing had the capacity to become automatically thinner or thicker if the surroundings heated up or cooled down? Researchers at UC San Diego are exploring how printed electronics could help achieve this.

Cranking up the heat or the air conditioner have been common responses to changes in temperature for decades. But what if the microclimate could be controlled at the individual level? What if clothing had the capacity to become automatically thinner or thicker if the surroundings heated up or cooled down? Researchers at UC San Diego are exploring how printed electronics could help achieve this. Their efforts are supported with a 2.6 million USD grant from the U.S. Department of Energy’s Advanced Research Projects Agency – Energy (ARPA-E).

The project, named ATTACH (Adaptive Textiles Technology with Active Cooling and Heating), is led by Joseph Wang, distinguished professor of nanoengineering at UC San Diego. While having a shirt that reacts to changes in outside temperatures is certainly comfortable for the person wearing it, Wang and his team had bigger topics in mind.

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“The idea was spurred from the need to decrease energy costs associated with heating and cooling our homes”, wrote Rajan Kumar, a Ph.D. student in the Department of NanoEngineering at the UC San Diego Jacobs School of Engineering in an email interview. “We have calculated that for each degree change in temperature in a consumer’s home, the energy costs increase by 6 to 8 %. Instead of heating the entire home, the ATTACH project will focus on heating or cooling the individual to provide better comfort and reduce costs significantly.”

The smart fabric is designed to keep the temperature of the wearer’s skin at 93° F or 33.8° C by adapting to temperature changes in the room. While the whole shirt changes according to changes in temperature by becoming thicker or thinner with the help of polymers that shrink or expand, the researchers also inserted thermoelectrics that are printable and are incorporated into specific spots of the smart fabric. The thermoelectrics regulate the temperature on “hot spots”—such as areas on the back and underneath the feet—that tend to get hotter than other parts of the body when a person is active.

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The smart fabric provides its own power through biofuel cells that can convert sweat into electrical power. Rechargeable batteries are also integrated into the textile structures. All of these parts, the batteries, thermoelectrics and biofuel cells, are printed using the technology developed in Wang’s lab to make printable wearable devices. The parts will be thin, stretchable and flexible to ensure that the smart fabric is not bulky or heavy and can be washed and worn like normal fabrics.

The team uses a semi-automatic screen printer, which is commonly utilized to print thick films of conductive inks, for example for RFID tags. “The screen printing technology in our lab uses a metal sheet that is cut with the design of any desired shape — this is called a stencil. The stencil can be applied to any substrate, in this case, adaptive textile clothing”, explains Kumar “We hope to ultimately use this printing technology to mass fabricate and integrate multiple electronic devices onto clothing in a cost-effective manner.”

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The greatest challenge of this project is how to integrate all these technologies into fashionable clothing that consumers love to wear. So far, Kumar says, computing devices have become integrated into almost every part of our daily lives. “Yet our clothing still seems to be left in the Stone Age”, he adds. That’s one reason why he finds the work he does with the team so intriguing: “Our technology has the promise not only to improve current printed electronic devices, but to revolutionize the way we use and interact with our clothing.”